mmc: core: clarify how to use post_req in case of errors

The err condition in post_req() is set to undo a call made to pre_req()
that hasn't been started yet.  The err condition is not set if an MMC
request returns an error.

Signed-off-by: Per Forlin <per.forlin@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 4c4bddf5ef61..340cc0c9409f 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -109,6 +109,9 @@ struct mmc_host_ops {
          * It is optional for the host to implement pre_req and post_req in
          * order to support double buffering of requests (prepare one
          * request while another request is active).
+         * pre_req() must always be followed by a post_req().
+         * To undo a call made to pre_req(), call post_req() with
+         * a nonzero err condition.
          */
         void    (*post_req)(struct mmc_host *host, struct mmc_request *req,
                             int err);